1. Field of the Invention
The present invention relates to a micro-electro-mechanical optical cross connect switch and, in particular, to a mirror inclination and rotation control for the switch.
2. Description Of Related Art
Micro Electro Mechanical Systems (hereinafter, MEMS) are miniature machines manufactured using silicon integrated circuit fabricating technologies (e.g., with film layers of polycrystaline silicon, silicon nitride and dioxide and gold deposited and patterned) and other technologies that result in miniature mechanically moveable devices. The last step (or latter steps) involve selective etching to remove some material that leaves movable members. For example, a miniature deflectable cantilever member may be manufactured on a substrate so that deflection can be controlled by electrostatic forces. A gold film mirror mounted on the cantilever member can selectably deflect a beam of light.
Scientists xe2x80x9chave built a microscopic optical switch that works like a child""s seesaw and demonstrates the world""s first practical optical-switching technology using micro-electro-mechanical systems (MEMS),xe2x80x9d according to one press release titled xe2x80x9cBell Labs scientist unveils xe2x80x98seesawxe2x80x99 optical switch, world""s first practical micro-electro-mechanical optical switching technology,xe2x80x9d News and Investor Info Press Release, Feb. 23, 1999. The xe2x80x9cseesawxe2x80x9d of the experimental switch is a tiny, pivoting bar with a gold plated mirror on one end. A lightwave enters the switch from an input optical fiber and exits the switch from an output optical fiber. The input and output optical fibers are co-axially configured with a gap between the ends and the mirrored end of the bar being disposed in the gap. The xe2x80x9cseesawxe2x80x9d is normally oriented to permit lightwaves to freely transit from the input fiber to the output fiber. However, to operate the switch, a voltage is applied to the other end of the bar, beneath an attached plate, so that electrostatic forces pull the plate down and lift the mirrored end of the bar so that the mirror interrupts the incoming lightwave before it reaches the output fiber. Such a switch is a single pole, single throw normally closed switch. Other means are known to perform optical switching by moving a mirror into a particular position, either by linear or rotary motor, to reflect an optical beam into a receiving optical fiber.
However, the prior art does not describe a means to adjust the angle of the mirrors to align input and output fibers so as to correct for misalignments that may arise due to manufacturing misalignment and wear.
It is an object of the present invention to overcome limitations in the prior art. It is a further object of the present invention to adjust the angle of the mirrors in a MEMS optical switch. It is yet another object to measure an output position of a mirror reflected beam to provide mirror adjustment feedback.
These and other objects are achieved in an optical switch that includes an input optical fiber, an output optical fiber and a mirror that is adjustable and reflects a lightwave signal from the input optical fiber into the output optical fiber. In a variant, the switch further includes a control circuit to sense a misalignment error and to adjust the mirror to correct the misalignment error. The misalignment error may be either an inclination misalignment error, a rotation misalignment error or both.
A GRISM is a class of optical devices that combine the physical and spectral dispersion properties of a prism with that of a diffraction grating.
These and other objects are achieved in an alternative embodiment where an optical switch includes an input optical fiber that includes an input core and an input cladding, an output optical fiber that includes an output core and an output cladding, an input GRISM to insert a calibration signal into the input cladding and a mirror that is adjustable. The mirror reflects a lightwave signal from the input core into the output core and reflects the calibration signal from the input cladding into the output cladding. The optical switch further includes an output GRISM to extract the calibration signal from the output cladding. In a variant, the optical switch further includes a control circuit to sense a misalignment error based on the extracted calibration signal. The misalignment error includes an inclination misalignment error or a rotation misalignment error or both. The control circuit includes circuitry to adjust the mirror to correct the misalignment error.
These and other objects are achieved in another alternative embodiment where an optical switch includes an input optical fiber, an output optical fiber and a rotatable mirror that has diffraction gratings etched thereon. The mirror reflects a lightwave signal from the input optical fiber into the output optical fiber. The optical switch further includes a control circuit to adjust a rotation angle of the mirror to select a wavelength that can be diffracted into the output optical fiber according to a spacing of the diffraction gratings.